1. Field of the Invention
The present invention relates, most generally, to methods for forming semiconductor structures, and more particularly to methods for forming interconnect structures of integrated circuits.
2. Description of the Related Art
With advances in electronic products, semiconductor technology has been applied widely in manufacturing memories, central processing units (CPUs), liquid crystal displays (LCDs), light emitting diodes (LEDs), laser diodes and other devices or chip sets. In order to achieve high-integration and high-speed requirements, dimensions of semiconductor integrated circuits have been reduced and various materials, such as copper and ultra low-k dielectrics, have been proposed along with techniques for overcoming manufacturing obstacles associated with these materials and requirements. In addition, interconnect structures with air gaps have been proposed and used to further reduce dielectric constants of layers and/or spaces between two neighboring conductive lines or layers.
FIG. 1 is a schematic drawing showing a traditional interconnect structure with air gaps. Copper lines 120 are formed over the substrate 100. Air gaps 110 are formed between the copper lines 120. A dielectric layer 130 is formed over the air gaps 110 to seal the air gaps 110 between the copper lines 120. A dielectric layer 150 and an etch stop layer 140 are sequentially formed over the dielectric layer 130. Dual damascene openings 160 are formed within the dielectric layer 150 and the etch stop layer 140, exposing the top surface (not labeled) of the copper lines 120 such that a copper layer can be formed within the dual damascene openings 160 for electrical connection.
The air gaps 110 have a dielectric constant k “1.0.” The interconnect structure with the air gaps 110 shown in FIG. 1 thus desirably reduces parasitic capacitances between the copper lines 120. Therefore, the air-gap interconnect conductive structure has a desired resistance-capacitance (RC) time delay such that high-speed integrated circuits can be achieved.
Based on the foregoing, structures and methods for forming interconnect structures with air gaps are desired.